Message6314

I created a new branch issue718-backup out of branch issue718. Afterwards, I
closed branch issue718 and I created a new branch with the same name out of
default. To that new branch, I imported patches that contain the meaningful
changes from the old issue718 branch.
In the new branch the changes affect options only. The type of member variables
are not changed from Heuristic to Evaluator. Also the functions are not moved
from Heuristic to Evaluator. Instead, I chose to cast Evaluator to Heuristics if
necessary and call an InputError if the Evaluator that is passed through options
is not a Heuristic. For example the InputError is called if someone puts an
Evaluator as preferred operator heuristic because an Evaluator does not provide
preferred operators.
After our live discussions I decided for these changes to the code, because they
seemed most minimalistic and safe to me.
A new pull request can be found here:
https://bitbucket.org/manuel_h/downward/pull-requests/4/issue718/diff